Process for producing ceramic fiber-reinforced composite material and ceramic fiber-reinforced composite material

ABSTRACT

To obtain a ceramic fiber-reinforced composite material, by melt-infiltrating a composite material substrate obtained by forming ceramic fibers into a composite with a matrix formed of an inorganic substance, with an alloy having a composition that is constituted by a disilicate of at least one or more transition metal among transition metals that belong to Group 3A, Group 4A or Group 5A of the Periodic Table and silicon as the remainder, and having the silicon content ratio of 66.7 at % or more.

BACKGROUND

1. Technical Field

The present invention relates to a process for producing a ceramicfiber-reinforced composite material that is formed by infiltrating theentirety or a part of pores that are present in a composite materialsubstrate obtained by forming ceramic fibers into a composite with amatrix (base material) formed of an inorganic substance, with aninfiltrating material, and can be used at a high temperature, and to aceramic fiber-reinforced composite material.

2. Related Art

Generally, in ceramic fiber-reinforced composite materials, a specialinterface layer is required for an interface between ceramic fibers anda matrix so as to control the adhesion strength between the ceramicfibers and matrix, and interface layers of hexagonal boron nitride(h-BN) or carbon (c) are most frequently used.

However, oxidation by water vapor in a temperature range of 800 to1,000° C. generates in boron nitride and oxidation by air in atemperature range of 800° C. or more generates in carbon, to therebyinhibit the high temperature properties of the ceramic fiber-reinforcedcomposite material.

Furthermore, formation of a matrix in a ceramic fiber-reinforcedcomposite material is conducted by a chemical vapor deposition process(CVD), a chemical vapor infiltration process (CVI), a ceramic precursorinfiltration-pyrolysis process (PIP), a reactive sintering process (RS)or the like, but pores (voids) remain in either process.

For example, in the infiltration-pyrolysis process of a ceramicprecursor, decrease of weight and volume generates in the process offorming a ceramic by heat decomposition of the precursor.

In the chemical vapor deposition process and chemical vapor infiltrationprocess, the diffusion of reaction gas into the inside of a preform ofceramic fibers is inhibited according to the growth of a matrix, andthereby pores remain.

In the reactive sintering process, remaining of pores in accordance withthe volumetric shrinkage during reactive sintering occurs.

Due to such phenomena, it is impossible to completely fill a matrix in aceramic fiber-reinforced composite material, and generally, pores of atleast several percent by volume to several ten percent by volume or moreremain.

These pores become entry pathways for gases (air and water vapor) thatoxidize the interface layer to thereby cause decrease of the adhesionstrength between the ceramic fibers and matrix, and the residual poresthemselves become one of the causes of the deterioration of themechanistic properties of the ceramic fiber-reinforced compositematerial.

In order to solve these problems, for example, a technique includinginfiltrating pores of a ceramic-based composite material with glass tothereby suppress oxidation at an interface layer is known (see JapanesePatent Application Laid-Open (JP-A) No. 10-259070 and the like).

Furthermore, a technique including forming a silicon carbide matrix by areactive sintering process by infiltrating a preform of ceramic fiberswith a carbon powder, and melt-infiltrating the preform with metallicsilicon, to thereby suppress the deterioration of an interface layer isknown (see JP-A Nos. 10-59780, 11-263668 and the like).

Furthermore, a technique including obtaining a silicon carbidefibers/silicon-silicon carbide composite material by molding a moldedarticle including silicon carbide fibers and silicon carbide particlesby using metallic silicon as a binder to thereby suppress thedeterioration of an interface layer and improve the mechanisticproperties is known (see JP-A No. 10-167831 and the like).

SUMMARY

However, the technique known in the above-mentioned JP-A No. 10-259070has a problem that, since the glass is chemically unstable in atemperature range of 1,000° C. or more, the material is deterioratedover time by use in that temperature range and thus has low durability.

Furthermore, the technique also has a problem that the material cannotbe applied in a high temperature range over 1,300° C. since melting andvaporization of the glass generate.

The techniques known in the above-mentioned JP-A Nos. 10-59780 and11-263668 have a problem that it is necessary to form a reactionprotective layer by a chemical vapor deposition process (CVD process) orthe like on the surface of the ceramic fibers so as to prevent thedeterioration of the ceramic fibers and interface layer due to directcontact of the molten silicon with the ceramic fibers or interface layerduring the production process, thereby the production steps becomecomplex.

Furthermore, in melt infiltration of silicon, it is necessary to heat toa temperature equal to or more than 1,414° C. that is the melting pointof silicon, generally to 1450° C. or more, but there is a problem thatheat decomposition occurs in this temperature range in many ceramicfibers, and thus the strength of the ceramic fibers is significantlydecreased.

For example, it is known that, when a heat treatment of amorphoussilicon carbide (SiC) fibers, amorphous alumina fibers or the like,which are generally used as ceramic fibers, is conducted at atemperature equal to or more than the production temperature of theseceramic fibers, heat decomposition proceeds and the mechanisticproperties are significantly inhibited.

Therefore, in the case when silicon is melt-infiltrated, there was aproblem that special ceramic fibers that are excellent in chemicalstability at a high temperature and extremely expensive (for example,Tyranno SA fibers (trade name: Ube Industries, Ltd.) and Hi-Nicalon TypeS fibers (trade name: Nippon Carbon Co., Ltd.), which are crystallinesilicon carbide fibers, and the like) may be used.

The technique known in the above-mentioned JP-A No. 10-167831 has aproblem that the strength property of the composite materialsignificantly decreases in a temperature range over 1,300° C. since thestrength property significantly depends on the metallic silicon as abinder.

Therefore, the present invention aims at providing a ceramicfiber-reinforced composite material obtained by forming ceramic fibersinto a composite with a matrix formed of an inorganic substance, whichsuppresses the deterioration of an interface layer, improves mechanisticproperties and has excellent durability even under a high temperature,even general ceramic fibers are used, without complicating theproduction steps.

A first aspect of the invention solves the above-mentioned problem byproviding a process for producing a ceramic fiber-reinforced compositematerial that is formed by infiltrating the entirety or apart of poresthat are present in a composite material substrate obtained by formingceramic fibers into a composite with a matrix formed of an inorganicsubstance, with an infiltrating material, wherein the infiltratingmaterial is an alloy having a composition that is constituted by adisilicate of at least one or more transition metal among transitionmetals selected from scandium, yttrium, titanium, zirconium, hafnium,vanadium, niobium and tantalum belonging to Group 3A, Group 4A or Group5A of the Periodic Table and silicon as the remainder, has a siliconcontent ratio (including the silicon in the transition metal disilicate)of 66.7 at % or more, and gives a melting point that is lower than thatof a single body of silicon, and the process comprises melt-infiltratingthe pores that are present in the composite material substrate with theinfiltrating material under a temperature environment at a temperatureequal to or more than the melting point of the alloy as the infiltratingmaterial.

A second aspect of the invention solves the above-mentioned problem byproviding the entirety or a part of the pores that are present in thecomposite material substrate with free carbon prior to the meltinfiltration, and reacting the alloy as the infiltrating material andthe free carbon in the pores during the melt infiltration to generatesilicon carbide and a carbide of the transition metal, besides theconstitution of the process for producing a ceramic fiber-reinforcedcomposite material of the first aspect.

Third and fourth aspects of the invention solve the above-mentionedproblem by that the melting point of the residual alloy that issolidified in the pores after the melt infiltration is higher than themelting point of the alloy as the infiltrating material prior to themelt infiltration, besides the constitutions of the processes forproducing a ceramic fiber-reinforced composite material of the first andsecond aspects.

Fifth, sixth, seventh and eighth aspects of the invention solve theabove-mentioned problem by that the above-mentioned ceramic fibers aresilicon carbide fibers, besides the constitutions of the processes forproducing a ceramic fiber-reinforced composite material of the first,second, third and fourth aspects.

A ninth aspect of the invention solves the above-mentioned problem byproviding a ceramic fiber-reinforced composite material that is formedby infiltrating the entirety or a part of pores that are present in acomposite material substrate obtained by forming ceramic fibers into acomposite with a matrix formed of an inorganic substance, with aninfiltrating material, wherein the infiltrating material is an alloyhaving a composition that is constituted by a disilicate of at least oneor more transition metal among transition metals selected from scandium,yttrium, titanium, zirconium, hafnium, vanadium, niobium and tantalumbelonging to Group 3A, Group 4A or Group 5A of the Periodic Table andsilicon as the remainder, has a silicon content ratio (including thesilicon in the transition metal disilicate) of 66.7 at % or more, andgives a melting point that is lower than that of a single body ofsilicon.

A tenth aspect of the invention solves the above-mentioned problem bythat silicon carbide and a carbide of the transition metal are presentin interface regions between the pores and the infiltrating material,besides the constitution of the ceramic fiber-reinforced compositematerial of the ninth aspect.

Eleventh and twelfth aspects of the invention solve the above-mentionedproblem by that the melting point of the residual alloy that issolidified in the pores after the melt infiltration is higher than themelting point of the alloy as the infiltrating material prior to themelt infiltration, besides the constitutions of the ceramicfiber-reinforced composite materials of the ninth and tenth aspects.

Thirteenth, fourteenth, fifteenth and sixteenth aspects of the inventionsolve the above-mentioned problem by that the above-mentioned ceramicfibers are silicon carbide fibers, besides the constitutions of theceramic fiber-reinforced composite materials of the ninth, tenth,eleventh and twelfth aspects.

According to the process for producing a ceramic fiber-reinforcedcomposite material of the first aspect and the ceramic fiber-reinforcedcomposite material of the ninth aspect, the melting point of the alloyas the infiltrating material becomes lower than 1,414° C. that is themelting point of silicon, by adjusting the silicon content ratio(including the silicon in the transition metal disilicate) of the alloyto 66.7 at % or more, thereby the temperature of the alloy as theinfiltrating material during the melt infiltration can be suppressed tobe low during the melt infiltration treatment of the infiltratingmaterial.

By this way, exposure of the ceramic fibers to a high temperature for along time can be suppressed, and decrease in the strength and durabilityof the ceramic fibers by heat can also be suppressed withoutcomplicating the production steps, even general ceramic fibers are used,and thus a ceramic fiber-reinforced composite material having excellentdurability even under a high temperature can be provided.

Furthermore, the alloy as the infiltrating material has a property thatthe melting point of the alloy simply decreases from 1,414° C. that isthe melting point of silicon as the silicon content ratio decreases from100 at %, and becomes the lowest at 85 to 95 at %, and the melting pointsimply increases in the range of 66.7 at % or more as the content ratiofurther decreases, and the melting points of the alloy are relativelylinear at the both sides of the lowest point and do not have extremeflexion point and singular point. Therefore, the melting point of thealloy during the melt infiltration treatment can be stably retained in aregion lower than the melting point of silicon.

Furthermore, by forming the ceramic fibers into a composite with amatrix formed of an inorganic substance in the step prior to the meltinfiltration of the infiltrating material, the effect of the directcontact of the alloy as the molten infiltrating material with theceramic fibers and interface layer can be completely prevented.

Moreover, since the treatment is a sealing treatment on the pores thatare present in the composite material substrate, heat treatmentdistortion of the ceramic fibers which accompanies the melt infiltrationof the alloy as the infiltrating material generates significantlylittle, and thus the obtained ceramic fiber-reinforced compositematerial has a high dimensional accuracy.

Furthermore, the pores that are present in the composite materialsubstrate are sealed by the silicon alloy as the infiltrating material,and the like, and thus entry of gases (air and water vapor) that oxidizethe interface layer of the composite material substrate, thereby theoxidation resistance at the interface is significantly improved.

Furthermore, since a large amount of the transition metal disilicateremains together with metallic silicon after the infiltration, muchmetal oxide is generated even oxygen and water vapor that are present inthe environment enter, and thus more excellent oxidation resistance isshown than in the case when only silicon dioxide is generated.Therefore, an excellent effect is exerted also from the viewpoint ofimprovement of oxidation resistance.

According to the constitutions of the second and tenth aspects, sincethe silicon carbide and a carbide of the transition metal are generatedon the interface regions between the infiltrating material and poresduring the melt infiltration of the infiltrating material, the carbidesfunction as a reaction protective layer for the interface region tothereby suppress the deterioration of the interface layer and improvethe mechanistic properties of the ceramic fiber-reinforced compositematerial.

Furthermore, since the silicon carbide and carbide of the transitionmetal are generated, the amount of the residual alloy that remains afterthe solidification is decreased, and thus the mechanistic properties canbe improved.

In addition, it becomes possible to change the ratio of the silicon andother transition metal in the residual alloy that remains after thesolidification from the ratio prior to the infiltration, by utilizingthe difference in the generation velocities of the silicon carbide andthe carbide of the transition metal according to temperature conditions.

According to the constitutions of the third, fourth, eleventh andtwelfth aspects, it becomes possible to accommodate up to the heatresistance limit of the composite material substrate itself withoutbeing affected by the melting point of the residual alloy that remainsafter the solidification in the practical use of the ceramicfiber-reinforced composite material, by increasing the melting point ofthe residual alloy that remains after the solidification by changing theratio of the silicon and other transition metal in the residual alloy.

According to the constitutions recited of the fifth, sixth, seventh,eighth, thirteenth, fourteenth, fifteenth and sixteenth aspects, theinterface regions between the pores in the composite material substrateand the infiltrating material are reinforced more, thereby thedeterioration of the interface layer is suppressed more and themechanistic properties of the ceramic fiber-reinforced compositematerial are improved more.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is the phase diagram (schematic view) of an exemplary embodimentof the alloy as the infiltrating material used in the present invention;and

FIG. 2 is the micrograph of the cross-sectional surface of the ceramicfiber-reinforced composite material of the present invention.

DETAILED DESCRIPTION

The specific embodiment of the process for producing a ceramicfiber-reinforced composite material of the present invention may be anyone as long as it is a process for producing a ceramic fiber-reinforcedcomposite material that is formed by infiltrating the entirety or a partof pores that are present in a composite material substrate obtained byforming ceramic fibers into a composite with a matrix formed of aninorganic substance, with an infiltrating material, wherein theinfiltrating material is an alloy having a composition that isconstituted by a disilicate of at least one or more transition metalamong transition metals selected from scandium, yttrium, titanium,zirconium, hafnium, vanadium, niobium and tantalum belonging to Group3A, Group 4A or Group 5A of the Periodic Table and silicon as theremainder, has a silicon content ratio (including the silicon in thetransition metal disilicate) of 66.7 at % or more, and gives a meltingpoint that is lower than that of a single body of silicon, and theprocess includes melt-infiltrating the pores that are present in thecomposite material substrate with the infiltrating material under atemperature environment at a temperature equal to or more than themelting point of the alloy as the infiltrating material.

Furthermore, the specific embodiment of the ceramic fiber-reinforcedcomposite material of the present invention may be any one as long as itis a ceramic fiber-reinforced composite material that is formed byinfiltrating the entirety or a part of pores that are present in acomposite material substrate obtained by forming ceramic fibers into acomposite with a matrix formed of an inorganic substance, with aninfiltrating material, wherein the infiltrating material is an alloyhaving a composition that is constituted by a disilicate of at least oneor more transition metal among transition metals selected from scandium,yttrium, titanium, zirconium, hafnium, vanadium, niobium and tantalumbelonging to Group 3A, Group 4A or Group 5A of the Periodic Table andsilicon as the remainder, has a silicon content ratio (including thesilicon in the transition metal disilicate) of 66.7 at % or more, andgives a melting point that is lower than that of a single body ofsilicon.

Namely, the ceramic fiber-reinforced composite material according to thepresent invention is obtained by pre-forming a composite material basematerial obtained by forming ceramic fibers as reinforcing fibers into acomposite with an oxide or an inorganic substance such as carbon as amatrix (base material), and melt-infiltrating pores or voids that remainin the composite material substrate with a transition metaldisilicate/silicon alloy as the infiltrating material.

The composite material substrate is preformed by forming a preform ofceramic fibers into a composite with an inorganic material as a matrix(base material) by a chemical vapor deposition process (CVD), a chemicalvapor infiltration process (CVI), a ceramic precursorinfiltration-pyrolysis process (PIP), a reactive sintering process (RS)or the like.

As the inorganic substance that forms the matrix, carbon, a nitride, acarbide, an oxide, a phosphate, a boride, crystallized glass or the likecan be applied.

The ceramic fibers can be applied to either long fibers or short fibers,and as reinforced forms of the preforms thereof, various states ofarrangement such as unidirectional reinforcement, woven fabriclamination, three-dimensional woven fabric and woven fabriclamination/suturation can be applied.

In order to react the melt-infiltrated transition metaldisilicate/silicon alloy and the free carbon in the pores to generatecarbides, as processes for providing free carbon to the inside of thepores in the composite material substrate prior to the infiltration,there are many techniques such as a chemical vapor deposition process(CVD), a chemical vapor infiltration process (CVI), aninfiltration-pyrolysis process (PIP) for a carbon precursor resin and aprocess for slurry infiltration of a carbon powder, and the free carbonas formed can also have various forms such as amorphous carbon,crystalline carbon, graphite, carbon nanotube and graphene.

A schematic drawing of a representative phase diagram of the transitionmetal disilicate/silicon alloy as the infiltrating material is shown inFIG. 1.

Here, T_(mp1) is the temperature at which the melting point of thesilicon alloy is the lowest, and T_(mp2) is the melting point of thetransition metal disilicate, and a predetermined component ratio withinthe composition range A is used as the composition of the transitionmetal disilicate/silicon alloy in the present invention.

These transition metal disilicate/silicon alloys have significantfeatures that the transition metal disilicates have melting points(T_(mp2)) that are higher than the melting point of silicon (1,414° C.),the transition metal disilicate/silicon alloys have melting points thatare lower than the melting point of silicon (1,414° C.), and the like.

The features of the transition metal disilicate/silicon alloys in abinary system, which are summarized for every transition metal, areshown in the following Table 1.

TABLE 1 Amount of Specific Lowest silicon (at %) Melting gravity ofmelting (at lowest point of transition point (° C.) melting point)disilicate (° C.) metal (g/cc) None 1414 Scandium 1000 84-86 (1230) 3.0Yttrium 1260 85-87 1850 4.5 Titanium 1330 84-86 1478 4.5 Zirconium 137087-89 1620 6.5 Hafnium 1330 91-93 1543 13.3 Vanadium 1400 95-97 1677 6.0Niobium 1400 96-98 1940 8.6 Tantalum 1375 92-94 2200 16.7

In general, an alloy having a low lowest melting point and containing atransition metal disilicate having a high melting point is desirable,and it is found that titanium, zirconium and hafnium, which aretransition metals in Group 4A of the Periodic Table, are preferable.

In vanadium, niobium and tantalum, which are transition metals in Group5A of the Periodic Table, the transition metal disilicate has a highmelting point, whereas the transition metal disilicate/silicon alloy hasa slightly high melting point. Conversely, in the cases of scandium andyttrium, which are transition metals in Group 3A of the Periodic Table,the transition metal disilicate/silicon alloy has a low melting point,whereas the transition metal disilicate tends to show a slightly lowmelting point.

Among these, hafnium, zirconium and yttrium can be preferably used asthe transition metal disilicate/silicon alloy for infiltration since thetransition metal disilicate/silicon alloy has a low melting point, thetransition metal disilicate has a high melting point, and the transitionmetal disilicate has relatively excellent oxidation resistance.

For example, in the case of a hafnium disilicate/silicon alloycontaining 8 to 9 at % of hafnium, the melting point is decreased toabout 1,330° C. at the lowest, and thus it becomes possible to decreasethe melt infiltration temperature to about 1,380° C.

At this temperature, for example, even general silicon carbide fibers(Tyranno ZMI fibers and Lox-M fibers (trade names: Ube Industries,Ltd.)) or the like are applied as ceramic fibers, it becomes possible tosignificantly suppress the decrease in the strength of the fibers in themelt infiltration step.

By providing the entirety or a part of the pores that are present in thecomposite material substrate with free carbon prior to the meltinfiltration, for example, when the pores are melt-infiltrated with thehafnium disilicate/silicon alloy containing 8 to 9 at % of hafnium, thesilicon in the alloy reacts with the free carbon present in the pores togenerate silicon carbide, whereas the reaction amounts of the hafniumand free carbon in the alloy is relatively small, and thus the amount ofthe hafnium in the hafnium disilicate/silicon alloy changes little.

Therefore, the silicon on the hafnium disilicate/silicon alloydecreases, and the melting point in the hafnium disilicate/silicon alloyconsequently increases according to the phase diagram shown in FIG. 1.

It is also possible to bring the melting point of the residual hafniumdisilicate/silicon alloy after the infiltration close to the meltingpoint (T_(mp2)) of hafnium disilicate by suitably adjusting the amountof the free carbon, the infiltration temperature and the infiltrationtime, and the melting point of the residual hafnium disilicate/siliconalloy can be increased to about 1,400° C. that is the melting point ofsilicon.

EXAMPLES

Next, the exemplary embodiments of the process for the production of aceramic fiber-reinforced composite material and the ceramicfiber-reinforced composite material of the present invention will beexplained in more detail.

As the ceramic fibers, amorphous silicon carbide fibers formed of achemical composition of Si—Zr—C—O (Tyrrano ZMI fiber (trade name: UbeIndustries, Ltd.) which had been woven into an orthogonalthree-dimensional woven fabric having a shape of about 120 mm×120 mm×4mm was used as a preform.

The fiber volume fractions of the woven fabric are 20%, 20% and 0.3%,respectively, in the X, Y and Z directions.

A carbon layer having a thickness of about 0.1 to 0.3 μm was firstformed on the fiber surface on the preform of the amorphous siliconcarbide fibers by a chemical vapor deposition process (CVI process)using propane (C₃H₈).

Furthermore, SiC having a thickness of 5 to 10 μm was deposited on thefiber surface by a CVI process using silicon tetrachloride (SiCl₄) andpropane (C₃H₈) to form a matrix, to thereby form a composite materialsubstrate that is a premolded product. The composite material substratehas a bulk density of about 1.8 g/cc and a pore rate of about 25%.

The composite material substrate that had been pre-formed in this waywas cut into about a width of 30 mm×a thickness of 4 mm×a length 50 mmand used as a sample, and the powders of the transition metaldisilicate/silicon alloys having the respective composition shown inExamples 1 to 6 in the following Table 2 were each applied thereto byusing a spray glue (Spray Glue 77 (trade name: manufactured by 3M)).

The powder was applied five times to every surface of the sample, andthe sample to which the transition metal disilicate/silicon alloy hadbeen applied was put into a carbon crucible and heated in vacuum byusing a carbon heater furnace to infiltrate the pores in the compositematerial substrate with the transition metal disilicate/silicon alloy togive a ceramic fiber-reinforced composite material (Examples 1 to 6).

The temperatures for the infiltration treatment were each preset to atemperature that is about 50° C. higher than the melting point, as shownin the following Table 2, and the heat treatment time was 1 hour.

Furthermore, an example in which the infiltration treatment with theinfiltrating material was not conducted (Comparative Example 1), anexample in which silicon was melt-infiltrated in vacuum at 1,430° C.(Comparative Example 2), and an example in which silicon wasmelt-infiltrated in vacuum at 1,470° C. (Comparative Example 3) weredefined as comparative examples.

TABLE 2 Matrix Free Content ratio of Impregnation composition carboninfiltrating tempreature after infiltration in pores material (at %) (°C.) (pore parts) Comparative None (Impregnation Example 1 material wasabsent) Comparative None Si(100) 1470 Si Example 2 Comparative NoneSi(100) 1430 Si Example 3 Example 1 None Si(92)—Hf(8) 1380 HfSi₂ + SiExample 2 None Si(88)—Hf(12) 1380 HfSi₂ + Si Example 3 NoneSi(88)—Zr(12) 1420 ZrSi₂ + Si Example 4 None Si(86)—Y(14) 1310 YSi₂ + SiExample 5 None Si(85)—Ti(15) 1380 TiSi₂ + Si Example 6 None Si(93)—Ta(7)1420 TaSi₂ + Si Example 7 Present Si(88)—Hf(12) 1420 HfSi₂ + Si +(carbon SiC black) Example 8 Present Si(88)—Hf(12) 1420 HfSi₂ + Si +(phenol SiC resin char)

A bending test piece of 4×4×length 50 mm was processed from each ceramicfiber-reinforced composite material, and bending tests and measurementsof pore rates at 1,200° C. and 1,300° C. under room temperature in argonwere conducted.

Furthermore, a sample of 4×4×4 mm was cut out, and the change in theweight by oxidation was measured by a thermal gravimetry in the air.

The measurement conditions were an airflow amount of 100 mL/min and atemperature raising velocity of 10° C./min, and the temperature wasretained at 1,200° C. for 5 hours and the change in the weight duringthat time (increase in amount by oxidation) was measured.

The obtained results are shown in the following Table 3.

TABLE 3 Increase in amount by Bending strength (MPa) oxidation DensityPore rate Room (mg/mm²) (g/cc) (vol. %) temperature 1200° C. 1300° C. —Comparative 1.80 24.1 253 172 124 0.06 Example 1 Comparative 2.45 2.9 8545 38 0.06 Example 2 Comparative 2.10 16.7 140 65 35 0.06 Example 3Example 1 2.60 3.4 250 188 162 0.02 Example 2 2.75 2.0 255 197 175 0.02Example 3 2.55 1.8 180 160 142 0.05 Example 4 2.50 2.6 245 185 162 0.01Example 5 2.45 3.1 249 175 151 0.06 Example 6 2.62 2.2 170 146 121 0.07Example 7 2.65 2.0 242 206 181 0.02 Example 8 2.60 3.9 248 210 175 0.02

In Comparative Example 1 in which the infiltration treatment with theinfiltrating material was not conducted, the pore rate was high as24.1%, whereas the bending strength was a tolerable value of about 253MPa.

In Comparative Example 2 in which the sample was melt-infiltrated withsilicon (Si: 100%) under vacuum at 1,470° C., the bending strength wasdecreased to 85 MPa in accordance with the decrease in the strength dueto thermal decomposition of the ceramic fibers during the infiltrationtreatment.

In the case of Comparative Example 3 in which the infiltrationtemperature was set to 1,430° C. that is slightly higher than themelting point of silicon (1,414° C.) so as to suppress the decrease inthe strength of the ceramic fibers, the pore rate was slightly high asabout 16.7% due to the high viscosity of the molten silicon, i.e.,infiltration could not be sufficiently conducted.

Furthermore, even the heat treatment temperature was decreased to 1,430°C., slight decrease in the strength due to thermal decomposition of theceramic fibers was also observed.

On the other hand, in either of Examples 1 to 6 of the presentinvention, since the melt infiltration temperature could be suppressedto 1,420° C. or less at most, thermal decomposition of the ceramicfibers was significantly suppressed, and thus a ceramic fiber-reinforcedcomposite material having a high bending strength could be obtained.

Furthermore, the pore rate was 4% or less at the most and thus theinfiltration property was extremely fine. Specifically, it is understoodthat, in the cases of the transition metal disilicate/silicon alloyscontaining hafnium and yttrium, respectively, the increase in amount byoxidation at 1,200° C. is also decreased, and thus materials also havingexcellent oxidation resistance can be obtained.

As Example 7 in the present invention, a pre-formed composite materialsubstrate as in the above-mentioned Examples 1 to 6 was subjected to avacuum infiltration treatment and a dry-curing treatment at 120° C., byusing an aqueous solution containing 19.2 wt % of carbon black had beendispersed therein (Aqua-Black 162 (trade name: Tokai Carbon Co., Ltd.))to which 0.5 wt % of an acrylic resin-based binder (Merposol (tradename: Matsumoto Yushi-Seiyaku Co., Ltd.) had been added.

These vacuum infiltration/drying/curing treatments were repeatedlyconducted five times to thereby disperse carbon black in the pores togive a composite material substrate, and the composite materialsubstrate was melt-infiltrated with a hafnium disilicate/silicon alloyhaving a composition of Si (88 at %)-Hf (12 at %) in vacuum at 1,380° C.to give a ceramic fiber-reinforced composite material.

FIG. 2 is the micrograph of the cross-sectional surface of the obtainedceramic fiber-reinforced composite material.

Most of the pores became SiC that was generated by the reaction betweenthe filled carbon and the silicon in the melt-infiltrated hafniumdisilicate/silicon alloy, and the gaps thereof were filled with theresidual hafnium disilicate/silicon alloy.

As a result of an analysis of the crystal phase of this by an X-raydiffractometry, the peak of HfSi₂ was not changed whereas the peak ofmetallic Si was extremely small.

Furthermore, the peak of crystalline SiC was significantly increased,whereas the peak of HfC was observed little.

Accordingly, it was found that a considerable part of Si in the hafniumdisilicate/silicon alloy became SiC by the reaction with the free carbonin the pores, and most of the hafnium disilicate/silicon alloy phaseremaining in the material was HfSi₂.

Furthermore, no decrease in the bending strength due to metalinfiltration was observed, and thus a fine composite material could beobtained.

As Example 8 in the present invention, a pre-formed composite materialsubstrate as in the above-mentioned Examples 1 to 6 was soaked in asolution obtained by diluting a novolak-type phenol resin (J-325 (tradename: DIC Corporation)) with a solvent (methyl alcohol) at a ratio of1:1, vacuum deaeration for about 24 hours was conducted to infiltratethe pores with the phenol resin, the solvent was removed in a vacuumdrier at 100° C. for 5 hours, and the phenol resin was cured in the airat 160° C.

These vacuum infiltration/drying/curing treatments were repeatedlyconducted four times, and a heat treatment at 800° C. for 1 hour in anargon atmosphere was conducted to thereby carbonize the phenol resin togive a composite material substrate having pores containing carbon, andthe composite material substrate was melt-infiltrated with a hafniumdisilicate/silicon alloy having a composition of Si (88 at %)-Hf (12 at%) in vacuum at 1,380° C. to give a ceramic fiber-reinforced compositematerial.

Also in this Example 8, a ceramic fiber-reinforced composite materialhaving an excellent bending strength and contains a small amount of theresidual hafnium disilicate/silicon alloy could be obtained as inExample 7.

The ceramic fiber-reinforced composite material of the present inventioncan prevent the alloy as the infiltrating material, and the like frommelting at a high temperature and partially scattering to therebyinhibit the oxidation resistance, and thus is preferable for, forexample, movable parts that are used under high temperatures such asmoving blades in gas turbines, and also exerts excellent performances inany use such as improvement of bending strength and improvement ofanticorrosive property.

What is claimed is:
 1. A process for producing a ceramicfiber-reinforced composite material that is formed by infiltrating theentirety or a part of pores that are present in a composite materialsubstrate obtained by forming ceramic fibers into a composite with amatrix formed of an inorganic substance, with an infiltrating material,wherein the infiltrating material is an alloy having a composition thatis constituted by a disilicate of at least one or more transition metalamong transition metals selected from scandium, yttrium, titanium,zirconium, hafnium, vanadium, niobium and tantalum belonging to Group3A, Group 4A or Group 5A of the Periodic Table and silicon as theremainder, has a silicon content ratio (including the silicon in thetransition metal disilicate) of 66.7 at % or more, and gives a meltingpoint that is lower than that of a single body of silicon, and theprocess comprises melt-infiltrating the pores that are present in thecomposite material substrate with the infiltrating material under atemperature environment at a temperature equal to or more than themelting point of the alloy as the infiltrating material.
 2. The processfor producing a ceramic fiber-reinforced composite material according toclaim 1, comprising: providing the entirety or a part of the pores thatare present in the composite material substrate with free carbon priorto the melt infiltration; and reacting the alloy as the infiltratingmaterial and the free carbon in the pores during the melt infiltrationto generate silicon carbide and a carbide of the transition metal. 3.The process for producing a ceramic fiber-reinforced composite materialaccording to claim 1, wherein the melting point of the residual alloythat is solidified in the pores after the melt infiltration is higherthan the melting point of the alloy as the infiltrating material priorto the melt infiltration.
 4. The process for producing a ceramicfiber-reinforced composite material according to claim 2, wherein themelting point of the residual alloy that is solidified in the poresafter the melt infiltration is higher than the melting point of thealloy as the infiltrating material prior to the melt infiltration. 5.The process for producing a ceramic fiber-reinforced composite materialaccording to claim 1, wherein the ceramic fibers are silicon carbidefibers.
 6. The process for producing a ceramic fiber-reinforcedcomposite material according to claim 2, wherein the ceramic fibers aresilicon carbide fibers.
 7. The process for producing a ceramicfiber-reinforced composite material according to claim 3, wherein theceramic fibers are silicon carbide fibers.
 8. The process for producinga ceramic fiber-reinforced composite material according to claim 4,wherein the ceramic fibers are silicon carbide fibers.
 9. A ceramicfiber-reinforced composite material that is formed by infiltrating theentirety or a part of pores that are present in a composite materialsubstrate obtained by forming ceramic fibers into a composite with amatrix formed of an inorganic substance, with an infiltrating material,wherein the infiltrating material is an alloy having a composition thatis constituted by a disilicate of at least one or more transition metalamong transition metals selected from scandium, yttrium, titanium,zirconium, hafnium, vanadium, niobium and tantalum belonging to Group3A, Group 4A or Group 5A of the Periodic Table and silicon as theremainder, has a silicon content ratio (including the silicon in thetransition metal disilicate) of 66.7 at % or more, and gives a meltingpoint that is lower than that of a single body of silicon.
 10. Theceramic fiber-reinforced composite material according to claim 9,wherein silicon carbide and a carbide of the transition metal arepresent in interface regions between the pores and the infiltratingmaterial.
 11. The ceramic fiber-reinforced composite material accordingto claim 9, wherein the melting point of the residual alloy that issolidified in the pores after the melt infiltration is higher than themelting point of the alloy as the infiltrating material prior to themelt infiltration.
 12. The ceramic fiber-reinforced composite materialaccording to claim 10, wherein the melting point of the residual alloythat is solidified in the pores after the melt infiltration is higherthan the melting point of the alloy as the infiltrating material priorto the melt infiltration.
 13. The ceramic fiber-reinforced compositematerial according to claim 9, wherein the ceramic fibers are siliconcarbide fibers.
 14. The ceramic fiber-reinforced composite materialaccording to claim 10, wherein the ceramic fibers are silicon carbidefibers.
 15. The ceramic fiber-reinforced composite material according toclaim 11, wherein the ceramic fibers are silicon carbide fibers.
 16. Theceramic fiber-reinforced composite material according to claim 12,wherein the ceramic fibers are silicon carbide fibers.